1. Field of the Invention
This invention relates to an improvement of a speed shifting time control device of an automatic transmission.
2. Description of the Prior Art
As a speed shifting time control device of an automatic transmission, such devices as disclosed by U.S. Pat. No. 4,283,970 and Japanese Patent Application Publication Gazette No. 63-3183, for example, have been known. According to these devices, time required for speed shifting (hereinafter referred to as "speed shifting time") which is done by operation of friction elements is measured and line pressure to be supplied to the friction elements is learningcontrolled so that the above speed shifting time becomes a target value at the succeeding speed shifting.
The target value of speed shifting time mentioned above is so set beforehand that speed shifting shock can be restricted effectively and durability of friction elements to sliding can be ensured.
However, it has been found that in the case where the target value of speed shifting time is set at the specified value, the following defects are experienced, namely, if the oil temperature of line pressure is high, the temperature of friction elements is easy to rise due to heat generated by sliding of friction elements (as compared with the case of low oil temperature in the same speed shifting time) and therefore, under the condition of high oil temperature durability of friction elements is easy to deteriorate and their reliability is reduced.